As a circular information recording medium, an optical disc is known. Recently, as the recording density and the capacity of optical discs have been increased, it has become important to guarantee high reliability of the optical discs. In order to guarantee high reliability, an optical disc apparatus performs adjustment processing for obtaining recording conditions which are used when information is recorded on the optical disc mounted thereon. Adjustment processing includes recording power adjustment for obtaining an optimum recording power condition of a semiconductor laser for emitting light toward the optical disc.
Hereinafter, a general structure of an optical disc and conventional recording power adjustment will be described.
FIG. 13 shows a structure of a general disc medium. The disc medium can be a recordable optical disc such as, for example, a DVD-R or a DVD-RW. A circular optical disc 1301 has a plurality of tracks 1302 arranged concentrically or spirally. Each track 1302 is divided into a plurality of sectors 1303. The optical disc 1301 is roughly divided into a recording information area 1304, disc information areas 1305 and 1307, and a data recording area 1306.
The recording information area 1304 stores information for recording information on the optical disc 1301. The disc information areas 1305 and 1307 store parameters necessary for accessing a certain position of the optical disc 1301. The disc information area 1305 is also referred to as a lead-in area, and the disc information area 1307 is also referred to as a lead-out area. Data is recorded to or reproduced from the data recording area 1306.
FIG. 14 shows a structure of the recording information area 1304 shown in FIG. 13. The recording information area 1304 is provided at an inner position with respect to the disc information area 1305 (lead-in area). The recording information area 1304 includes a parameter calibration area 1401 (“PCA”; including power calibration area) used for, for example, performing recording power adjustment, and a recording management area 1402 (hereinafter, referred to as the “RMA”: Recording Management Area) for storing, for example, a recording power value obtained using the parameter calibration area 1401 and information regarding a recording state of the optical disc 1301. In the case of a DVD-R, for example, as shown in FIG. 14, the parameter calibration area 1401 is located in an inner portion of the recording information area 1304, and the RMA 1402 is located in an outer portion of the recording information area 1304. It should be noted that all optical discs do not have this structure.
FIG. 15 shows a structure of an ECC block and a sector. FIG. 15 illustrates the relationship between the ECC block which is a unit for calculating an error correction code, and the sector recorded in the optical disc 1301. In a larger capacity DVD, one ECC block includes 16 sectors in order to provide both a high error correction capability and low redundancy. In FIG. 15, one ECC block includes four sectors for the sake of convenience.
Portion (a) of FIG. 15 shows a structure of the ECC block. An ECC block includes main data arranged in 172 bytes×48 rows, an inner code parity PI obtained by calculating an error correction code on a row-by-row basis of main data (in a horizontal direction), and an outer code parity PO obtained by calculating an error correction code on a column-by-column basis of main data (in a vertical direction).
A code including an inner code parity and an outer code parity is generally referred to as a product code. The product code is part of an error correction system which is very useful against both random errors and burst errors (locally concentrated errors).
For example, it is assumed that a burst error for two rows is generated by a scratch in addition to random errors. A burst error is mostly a 2-byte error and thus is correctable by the outer code. In a column having many random errors, some of the random errors cannot be corrected by the outer code and remain as errors, which are mostly corrected by the inner code. Even if some of the errors cannot be corrected even by the inner code, those errors can be corrected using the outer code again.
In the field of DVD, use of such a product code provides sufficient error correction capability while suppressing the parity redundancy. In other words, the capacity for the user data can be increased by the amount corresponding to the parity redundancy suppressed.
Portion (b) of FIG. 15 shows a structure of the sector. The outer code parity of the ECC block is uniformly divided for each of the sectors row by row. As a result, one sector is formed of data of 182 bytes×13 rows.
In the following description, the term “block” refers to the above-described ECC block.
Next, recording power adjustment will be described.
Recording power adjustment is performed after an optical disc is mounted on an optical disc apparatus, before information is recorded on the optical disc, or each time characteristics of the optical disc or the optical disc apparatus are changed by a prescribed level or more due to a temperature change or other factors.
Recording power adjustment obtains an optimum recording power condition by performing recording to and reproduction from a parameter calibration area. The optical disc apparatus records information to areas other than the parameter calibration area of the mounted optical disc, using the recording power condition obtained by the recording power adjustment.
Next, how the parameter calibration area is used in recording power adjustment will be described.
In the case of a DVD-R, the parameter calibration area includes 7088 sectors. Among the 7088 sectors, the optical disc apparatus can use 6832 sectors for recording power adjustment. To the RMA, information is recorded on a block-by-block basis. The RMA includes 701 blocks.
The RMA stores border information on a border between an area of the parameter calibration area to which information has been recorded by recording power adjustment (hereinafter, referred to as the “used area”) and an area of the parameter calibration area to which no information has been recorded by recording power adjustment (hereinafter, referred to as the “unused area”). However, since the timing at which the RMA is updated is often synchronous with recording to the data recording area 1306, the border information is not necessarily the latest information. The border information is stored in the RMA on a block-by-block basis. Therefore, when, for example, recording power adjustment is performed on a sector-by-sector basis, the possibility that the border information stored in the RMA shows a correct border position is low. Accordingly, the border between the used area and the unused area needs to be directly detected.
In general, an RF amplitude detection processing section is used for directly detecting the border between the used area and the unused area. The RF amplitude detection processing section has a function of distinguishing the border between the used area and the unused area based on the level of the amplitude of a reproduction signal (RF amplitude).
FIG. 16 shows an exemplary structure of a parameter calibration area 1603 and an exemplary change in a recording power in conventional recording power adjustment performed using the parameter calibration area 1603.
The parameter calibration area 1603 is used from an outer periphery thereof on a sector-by-sector basis. For example, in one cycle of recording power adjustment, recording power condition information is recorded with the recording power being changed on a sector-by-sector basis from a sector located on the outer periphery. In FIG. 16, recording power condition information having five recording power conditions is recorded in five sectors in the parameter calibration area 1603.
Then, the recording power condition information recorded in the parameter calibration area 1603 is reproduced, and one of the five recording power conditions having the optimum reproduction state is obtained as a result of the recording power adjustment. The resultant recording power condition is used for recording information thereafter.
When a portion of the parameter calibration area 1603 is already used, i.e., when a portion of the parameter calibration area 1603 is a used area 1602, the RF amplitude detection processing section 561 detects the border between the used area 1602 and an unused area 1601. Recording power adjustment is performed using the unused area 1601 from the border. In this manner, the unused area 1601 becomes part of the used area 1602.
Hereinafter, how to use a parameter calibration area in a CD-WO will be described.
The recording format of a CD-WO is referred to as the “Orange Book”.
FIG. 17 shows a structure of a parameter calibration area 1703 in a conventional CD-WO. In FIG. 17, the parameter calibration area 1703 includes a test area 1701 used by recording power adjustment and a counter area 1702 showing the state of use of the test area 1701.
In the case of the CD-WO, for example, as one sector in the test area 1701 is used by the recording power adjustment, information is recorded in one sector in the counter area 1702. In this case, by detecting the state of use of the test area 1701 recorded in the counter area 1702, the border between an unused area 1701A and a used area 1701B in the test area 1701 can be distinguished.
In the conventional recording power adjustment shown in FIG. 16, the recording power in the recording power condition information gradually decreases from the outer periphery to an inner periphery of the parameter calibration area 1603 during one cycle of recording power adjustment.
When such recording power information is recorded in the parameter calibration area 1603, the recording power for performing the recording to an area at the border between the unused area 1601 and the used area 1602 decreases. Therefore, the RF amplitude detection processing section 561 cannot correctly detect the border between the used area and the unused area. In the case where the RF amplitude detection processing section 561 incorrectly detects a point in the used area as the border between the unused area 1601 and the used area 1602 in the next cycle of recording power adjustment, two different records of recording power adjustment are written, which reduces the precision of recording power adjustment.
In the parameter calibration area 1703 of the conventional CD-WO shown in FIG. 17, the counter area 1702 is used. Therefore, in the case where a plurality of sectors in the test area 1701 are consumed in one cycle of recording power adjustment, a plurality of sectors in the counter area 1702 are also consumed, which increases the area used for recording power adjustment.
The present invention has an objective of providing an information recording medium, an information recording and reproduction method, and an information recording and reproduction apparatus for clearly distinguishing a border between a used area and an unused area and also reducing an area of a parameter calibration area which is consumed by one cycle of recording power adjustment.